This invention relates to plasma generation for photolithography.
Photolithography systems are used to produce circuit patterns on semiconductor wafers. To produce devices with smaller dimensions, the optical resolving power of the photolithography system needs to be increased. Because optical resolving power is proportional to the wavelength of light, a light source with a shorter wavelength provides better optical resolution capability. Extreme ultraviolet (EUV) light may be utilized in manufacturing microelectronic semiconductor devices with feature sizes less than 100 nm. EUV light may be obtained from a synchrotron or from a high energy plasma. The plasma may be generated by focusing a high energy laser beam onto a stream of inert gas, such as Xenon. The plasma may also be produced by using electron emission in which electrodes emit electrons to ionize a gas to form a plasma. To energize the plasma to generate sufficient EUV light, the electrodes may have to operate at high temperatures with high power flowing through the electrodes. This causes the electrodes to emit particles that contaminate other components in the lithography system, such as a condenser lens. EUV light generated from Xenon plasma has a main component with a wavelength of about 13 nm. FIG. 1 shows an example of an EUV lithography system.